Possible vibration problems

[csmith]

I had my 94 750 st on hte lake for the first time this weekend.
It starts to vibrate at about 120ish km/h and gets worse all the way to an indicated 175 or so. I feel it mostly through my feet sitting in the normal position with feet forward in the foot wells.

They engine is fresh, welded crank and all. I don't think it is the engine because we I gas it it goes to a steady 8400ish rpms and stays there all the way from 0-175. No vibrations at lower speeds.

Very very fun to blow by all my buddies but I only made 2 passes because I didn't want something to come apart.

Any suggestions for what a rookie should look for?

Thanks
Corey

[csmith]

I found some loose/missing nuts for the motor mount on the left side. Right side seemed tight. I have to find a metric nut or 2 to tighten it back up and I can go try again but I'm worried it might be something else.
Or, could I have some sort of alignment problem now? Browsing around I see people trying to align there motor, would this be to the track?

Corey

[Exciter570]

Put on a new belt. A friend of mine experienced what you described on his RX-1, he was complaining all night, we went out on the lake were going 90-95mph, his belt snapped. He put the spare on and all vibration went away.

[csmith]

Thanks. Can't remember if there is a spare under the hood or not. If so I will try it. If not, should I park it till I buy a new one to be safe? I don't think I'd want to have something like that come apart at speed.

BTW, how fast do these things go? Mine is bone stock. I assume the long track will probably slow my top speed a bit due to the extra weight and drag.

I will search the forums here for belt recommendations. I know there have been several discussions already.

[Exciter570]

Don't use anything but a Yamaha belt, my friend with the RX-1 had an aftermarket belt on, I think it was an Ultimax 2 belt and he shredded it, enough said about that. As far as top speed, you should be able to see 110-115 on the speedo. Also, if you don't have a spare belt, get one, never drive without a spare, you never know when you may need it.

[BUBS SRX]

:agree: Good advice,Get the spare belt for sure.On the last Pine Stump run I experienced vibration for the last 5 miles of a ride with my 80 srx and looked imidiatly to the belt and it was missing about 7 inches of the under driver cogs from it.I change it and no vibrations just good salutations of a screamin old 440.

[mark the shark]

I agree with checking the belt first. It only takes a small bad spot to make a lot of vibration, especially at higher RPM. Check for missing cogs, a split between cogs, or a bad spot on the sides that ride on the clutch. If someone ever locked up the brakes, or spun the clutch while the track was frozen to the ground, it could cause a worn area on the side of the belt that would vibrate.
Shark

[AL P]

Ya know, I`ve kinda been experiancing the same thing. when my clutch engages, its real smooth, but when i speed up a bit, say around, ohh i dont know, 20 mph or so, i get this viabration down by my feet. But when i let off the gas it emediatly goes away, So I`ve ruled out anything to do with my track ect. but maybe I should take a look at my belt too?

[Reimond]

It could be bended drive axel also (through track)

[RedWhiteandBlue]

If not anything else, the speedo side drave shaft bearing is notorious for going south...Blue

[BUBS SRX]

:agree: Another good place to start if the belt is good

[AL P]

I think I`m gonna go in deep sometime this summer, and remove the drive shaft, inspect the chaincase, both drive shaft side bearing, and the one behind the clutch also.

[micultra]

Better late than never....I just had the same thing happen. My 8BU belt started to seperate,causing vibration at high speeds.I thought it would be noticeable at lower speeds when the clutch is ready to shift (belt spinning at high speeds) but the smallest amount of wear on the sides made a HUGE differeance. I'm No expert but I was amazed by the differance.
Just my thoughts
Charles

[csmith]

I looked at my belt....it looks in good shape. It is a Dayco (sp?) brand?
Now it may in fact be worn on the edges but the belt itself looked ok, no frays, missing lugs or anything.
I do have a spare belt, it is older looking. I am going to try it to at least see if it makes a difference. I couldn't ride it when I went to look at the belts.
Sucks no having the sled at home.

I'll follow-up when I know more.

[csmith]

Went to visit my sled today. Upon closer inspection my belt is in fact comming apart. It looks like the sides are worn enought that the threads are starting to show. This is allowing the outside flat part to separate from the inside coged part
.
Now for the real newbie question.
How do I change the belt. I assume the sled is supposed to come with some sort of special tool but mine did not. I have seen a guy change one on the trail with just his bare hands but I can't seem to figure out how or if that is even possible with a vmax. I _think_ your supposed to rotate or push back the inside sheave of the driven clutch?? I tried with my hands but no luck. There does appear to be 2 3/8" or so holes close together on the back side of the clutch that I bet some sort of tool is supposed to hook into.

Am I on the right track? Any suggestions?
I do have a tool box full of regular tools, a welder and an imagination...can I make what I need?

Corey

[csmith]

Answered most of my own questions with search...
http://www.vmax4.com/vbulletin/showthread.php?t=1707&page=2

So, I guess I was definitly on the right track. I could move the rear sheave clockwise a bit but not much, and it did not seem to want to slide backwards. The sled drives great so I assume both clutches are in good working order so maybe I just need to eat my wheaties and go giv'r another try? :)

[AL P]

I just put the rear bumper on the jack stand, so as to get the track off the floor, then I just walk the belt around/off the secondary. I start to pull the belt off at the top of the secondary, then I rotate the secondary clockwise until the belt comes off. no tools involved, and knock on wood, have`nt had a problem getting a belt off yet.
to better describe. look at the secondary as a clock. I pull the belt out towards the side pannel for example at about 10pm, then I turn the secondary clockwise, while all along pulling the belt towards me.